Avalição de nove espécies de leguminosas como hospedeiros alternativos de Phakopsora pachyrhizi Syd. & P.Syd.

Abstract

Soybean yield has been the main culture in Brazil for its cultivation area and grain yield, which puts Brazil in the second place in world greatest yield and in the first place in country exporter. Although, the potential of productive efficiency of that culture of 4,000 kg/ha, it is hart to reach. Among main factors, diseases predominated, with great importance for Asian rust that is caused by Phakopsora pachyrhizi Syd. & Syd. That disease is considered as one of the most destroyer disease due to its aggressively and rapid dissemination. As it is a biotrophic pathogen, multiplication and surviving of that fungus only occur in live tissues of plants, this way, “tiguera” soybean and alternative hosts can allow the surviving of the pathogen, which produces the initial inoculum for subsequent epidemicals. The present work aimed to evaluating the susceptible of nine species of leguminous as alternative hosts of P. pachyrhizi Syd. & P. Syd, the fungus that causes Asian rust. This work was carried out in two periods, one in B.O.D. chamber, temperature of 25ºC and R.H. 93%, and other at laboratory at 20(±2)°C, both two periods at Unit II of the Federal University of Great Dourados, Agrarian Science Institute, from March, 2006, to February, 2007. The following species were evaluated as green manure: common vetch (Vicia sativa L), green bean (Vigna unguiculata L.) Walp, fedegoso (Senna occidentalis) L., sunnhep (Crotalaria juncea L.), common bean (Phaseolus vulgaris L.), velvetbean (Mucuna aterrima L.) lablab bean (Dolichos lablab L.), jack bean (Canavalia ensiformes D.C.) and pea (Pisum sativum L). Every species that were inoculated with uredospore of P. pachyryhizi Syd. & P. Syd developed the symptoms; although, some species showed varied symptoms regarding to the number of harms and the presence of uredospore. Soybean, common bean, lablab bean and velvetbean showed fungal structures (uredospore) in both two conditions that the experiment was carried out, which shows that they have potential to hosting P. pachyrhizi Syd. & Syd. Jack bean, sunnhep, green bean and common vetch were considered susceptible plants, although those species showed be more exigent for sporulation of fungus.